How do I change read/write mode for a file using Emacs?

Question

If a file is set to read only mode, how do I change it to write mode and vice versa from within Emacs?

Answer 1

If you are looking at a directory of files (dired), then you can use Shift + M on a filename and enter the modespec, the same attributes used in the chmod command.
M modespec

See the other useful commands on files in a directory listing at http://www.gnu.org/s/libtool/manual/emacs/Operating-on-Files.html